1. Field of the Invention
The present invention relates to a retractable antenna and more particularly, to a dual-resonance retractable antenna.
2. Description of the Related Art
A regular retractable antenna is generally comprised of an outer tube and one or multiple inner tubes (for example, one outer tube 11 and one inner tube 12 as shown in FIG. 2). The inner tube can be moved out of the outer tube to extend the length of the antenna. However, conventional retractable antennas are simply for oscillation at a specific resonance frequency. By means of manually adjusting the length of the antenna, the frequency shift is controlled (see FIG. 1).
Following fast development of communication equipments, antenna is required to effectively achieve automation and to have multi-band multi-system capabilities for multiplex application. However, regular retractable antennas cannot achieve the requirements.
To solve the aforesaid problem, retractable antenna may be provided with a connector at the top side for the connection of an external antenna for signal transmission at a second frequency band. However, this arrangement is not to achieve the desired multi-frequency function by means of changing the arrangement of the retractable antenna itself but by means of attaching an external antenna for signal transmission at a second frequency band. This design is inconvenient in use.
Therefore, it is desirable to provide a retractable antenna that eliminates the aforesaid drawbacks.